Several procedures have been devised to surgically remove the obstruction and reestablish the blood flow. During these surgeries quantitative analysis is typically needed to evaluate blood flow. Currently, two evaluation methods are commonly used: fluorescein angiography and ultrasound color Doppler:
Fluorescein angiography in which fundus photos are taken after injecting the fluorescein dye into an arm vein is commonly used for both diagnosing retinal vein occlusion and evaluating treatments of retinal vein occlusion. Due to the medial opacities, fluorescein angiography is inadequate for both diagnosing and evaluating central retinal vein occlusion. Furthermore, in the fluorescein angiography procedure, multiple photos are taken by a camera with special filters, and they are analyzed subjectively by ophthalmologists. This method may not be suitable for instantaneously evaluating blood flow reestablishment during surgeries.
Some researchers have demonstrated the feasibility of measuring the blood flow velocities from the central retinal vein and artery behind the optic disc, using commercial color Doppler systems. These studies have shown a significant reduction in flow velocity in the central retinal vein in situations of central retinal vein occlusion (“CRVO”). These velocity variances may be used to diagnose CRVO. Ultrasound color Doppler techniques have typically operated at frequencies of less than 15 MHz. The corresponding achievable velocity resolutions of 1˜2 cm/s are insufficient for both the accurate clinical diagnosis and treatment evaluation, and the bulky ultrasound probe size introduces some setup complexities for the instantaneous flow evaluation during surgery. This method may not be suitable during an ophthalmologic surgery either.
A pulsed-wave Doppler system with a PMN-PT needle transducer has been developed to measure the blood flow velocity in selected retinal vessels. See, e.g., Emanuel J. Gottlieb, et al., “PMN-PT High Frequency Ultrasonic Needle Transducers for Pulsed Wave Doppler In The Eye,” 2005 IEEE Ultrasonics Symposium (IEEE 2005), the contents of which are incorporated herein by reference in their entirety.
Ultrasonic techniques have also been utilized in surgical procedures on the eye for imaging structure and/or tissue of a surgical site. See, e.g., U.S. Pat. No. 6,676,607 to de Juan, Jr. et al., the contents of which are incorporated herein by reference in their entirety.
While prior art techniques have proven useful for their respective intended purposes, they can present difficulties or limitations with respect to thrombolysis in retinal eye vessels. Such drawbacks have included the unwanted side effects on human tissue from high power intensities.